Method and apparatus for reducing extrusion start-up pressure

ABSTRACT

Extrusion start-up or peak pressure is reduced by initially commencing extrusion of the billet through a multiple aperture die and then closing off all but one of the said apertures in the die.

United States Patent Fuchs, Jr. Dec. 9, 1975 METHOD AND APPARATUS FOR[56] References Cited REDUCING EXTRUSION START-UP UNITED STATES PATENTSPRESS 2,723,028 11/1955 Carter 72/261 [75] Inventor: Francis JosephFuchs, Jr., Princeton 3,063,560 11/1962 Edgecombe 72/261 Junction, NJ.3,740,985 6/1973 Fuchs, Jr. 72/60 3,767,368 10/1973 Fuchs, Jr. 72/60[73] Ass1gnee: Western Electric Company, Inc.,

New York Primary ExaminerCarl E. Hall [22] Filed: Nov. 13, 1974Attorney, Agent, or FirmD. P. Kelley; A. S. Rosen [21] Appl. No.:523,403

[57] ABSTRACT [52] U.S. Cl. 72/60; 72/261; 72/271; Extrusion start-up orpeak pressure is reduced by ini- 72/284; 72/468 tially commencingextrusion of the billet through a [51] Int. Cl. B21D 22/10 l ipl p r redi n hen c ing ff l but ne [58] Field of Search 72/60, 61, 62, 63, 261,f he i aperture in the di 12 Claims, 5 Drawing Figures atent Dec. 9 1975Sheet 1 of 3 3,924,429

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. .w OhIm ZOGQEPXM TIME US. Pitfillt Dec.91975 Sheet 2 of3 3,924,429

METHOD AND APPARATUS FOR REDUCING EXTRUSION START-UP PRESSURE BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates,broadly speaking, to improved method and apparatus for reducingextrusion start-up or peak pressure. More specifically, this inventionrelates to method of and apparatus for eliminating or substantiallyreducing start-up or peak pressure, which may be encountered incommencing hydrostatic extru- SlOn.

2. Description of the Prior Art Various methods and means for extrudingbillet material through a die are not well known. See, for example, U.S.Pat. No. 3,667,267 (1973) to Fuchs, which teaches method and apparatusfor continuously hydrostatically extruding an elongated billet ofindefinite length to produce wire of indefinite length.

In commencing hydrostatic extrusion of certain materials to obtaincertain ratios of reduction, it has been noted that, when the nose ofthe billet enters and initially contacts the zone of deformation of thedie, the pressure of the extrusion fluid rises to a peak value untilextrusion commences. After extrusion commences, the pressure of theextrusion fluid falls to a lower, substantially constant, level known asthe run-out pressure. Thus, in the hydrostatic extrusion of copper atreduction ratios greater than 20, there is always a peak pressure at thecommencement of extrusion which is greater than the run-out pressure.

Although the peak pressure occurs only at the commencement of anextrusion operation, the pressure vessel for containing the extrusionoperation, the die, die stem and related components must be designed towithstand this peak pressure which may, in some instances, be as much as25 percent or more above run-out pressure, even though virtually theentire extrusion operation is performed at the lower run-out pressure.Thus, for virtually the entire extrusion operation, the pressure vessel,die, die stem and related components are overdesigned by as much as 25percent or more. From another point of view, elimination or substantialreduction of peak pressure permits much higher (e.g., by an order ofmagnitude or so) ratios of reduction in equipment of a given design andpressure capability. Indeed, for certain materials, ratios of reductionare now attainable which heretofore were not attainable because ofdesign limits on maximum pressure of equipment.

An example of the relationship between peak pressure and run-outpressure can be seen in the hydrostatic extrusion of a 0.300 inchdiameter copper billet to produce 0.013 inch diameter wire,respresenting a reduction ratio of 500, wherein the peak pressure in theextrusion fluid is 370,000 psi and the run-out pressure in the extrusionfluid is 280,000 psi.

More, as peak pressure is reached, extrusion commences with a burst ofspeed, which may be undesirable.

In non-hydrostatic extrusion operations, it has been noted that, forcertain materials and for certain ratios of reduction, the initialeffort required to commence the extrusion operation is substantially inexcess of the effort required to maintain the extrusion operation and,further, the extrusion operation may commence with an undesirable burstof speed.

Efforts have been made in the past to facilitate the extrusion ofbillets. In U.S. Pat. No. 2,630,220 (1953) to Sejournet, extrusion ofahot billet or ingot of steel is commenced by interposing between thefront end of the hot billet and the die a packet of glass fibers andglass plate, the glass melting under the heat of the billet andlubricating the die. In U.S. Pat. No. 3,345,842 (1967) to Richards, ahot billet is coated with a plurality of layers of glass of differentviscosity-temperature characteristics (e.g., by sequentially dipping theentire hot billet into tanks of the various molten glasses) and is thenextruded through a die. In the Sejournet and Richards patents, themolten glass acts as a lubricant.

More recently, eminently satisfactory solutions to the problem ofreducing extrusion start-up or peak pressure have been taught in U.S.Pat. No. 3,767,368 (1973) to Fuchs, U.S. Pat. No. 3,766,766 (1973) toFuchs and Venkatesan, U.S. Pat. No. 3,766,768 (1973) to Fuchs andVenkatesan, and U.S. Pat. No. 3,766,769 (1973) to Fuchs and Venkatesan.These solutions involve billet preparation, viz., the leading end of thebi]- let is provided with a nose of materials having a hardness gradientincreasing from a relatively low value (i.e., high softness) at thefront end of the nose to a value rearwardly thereof which may be equalto the hardness of the billet material.

The present invention represents a different approach to the problem ofelimination or substantial reduction of peak extrusion pressure, notinvolving preparation of the billet itself in the manner of the patentsmentioned in the preceding paragraph.

SUMMARY OF THE INVENTION One of the objects of this invention is toprovide improved method and apparatus for eliminating or substantiallyreducing peak effort ordinarily required to initiate an extrusionoperation.

A specific object of this invention is to provide improved method andapparatus for eliminating or substantially reducing peak pressure whencommencing a hydrostatic extrusion operation.

A further object of this invention is to provide improved method andapparatus for smoothly commencing hydrostatic extrusion.

Still other and further objects of this invention will become apparentduring the course of the following description and by reference to theaccompanying drawings and the appended claims.

Briefly, the billet is initially extruded through a multiple aperturedie and after extrusion has commenced, all but one of the apertures isclosed, extrusion being continued through the remaining open aperture.

BRIEF DESCRIPTION OF THE DRAWINGS Referring now to the drawings in whichlike numerals represent like parts in the several views:

FIG. 1 represents an idealized plot of extrusion effort (e.g.,hydrostatic extrusion fluid pressure) vs. time for two conditions, viz.,conventional extrusion and extrusion according to the present invention;

FIG. 2 represents a view in elevation of the entrance end of a multipleaperture die used with the present invention;

FIG. 3 represents a medial longitudinal section of the multiple aperturedie taken along the line 3-3 of FIG.

3 FIG. 4 represents a fragmentary view in elevation, partially in medialsection, of extrusion apparatus employing the valve plate of the presentinvention; and

FIG. represents a view in elevation of the valve plate from the line 33of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT In commencing the extrusion of abillet through a die for certain materials and certain ratios ofreduction, when the nose of the billet enters and initially contacts thezone of deformation of the die, and until extrusion of the billetthrough the die begins, the effort required to force the billet throughthe die peaks, and when the billet starts to extrude through the die,the effort required to continue the extrusion falls off to a lower orrun-out level. In terms of hydrostatic extrusion, when the nose of thebillet enters and initially contacts the zone of deformation of the die,and until extrusion of the billet through the die begins, the pressureof the extrusion fluid rises generally along curve 1 of FIG. 1 andreaches a maximum value 2. When the billet begins to extrude through thedie, the pressure of the extrusion fluid decreases, generally alongcurve 3, to a lower substantially constant level 4 known as the run-outpressure.

The difference between the maximum or peak pressure 2 and the run-outpressure 4 requires that the pressure vessel for containing theextrusion operation, the die, die stem and related components byoverdesigned for this high transitory condition.

The present invention eliminates or substantially reduces the peak ormaximum pressure 2, and permits the extrusion apparatus to be designedto operate substantially under the conditions of run-out pressure.

The multiple aperture extrusion die 5 with which the present inventionis employed will, advantageously, be of the type disclosed in a pendingUS. Pat. application filed concurrently herewith in the name of FrancisJoseph Fuchs, Jr. and entitled Multiple Aperture Die.

' Such a die 5 is shown in FIGS. 2 and 3 as comprising a conical mouth 6at the apex of which is provided a first die aperture 7 extendingthrough the said die 5 and communicating with passageway 8 at the rearend of the die 5. A plurality of second die apertures 9 is formedthrough the conical mouth 6 adjacent the entrance end 10 of the die 5,the said second die apertures 9 being radially equispaced around the die5 as shown particularly in FIG. 2. Each of the second die apertures 9 isprovided with a bevelled entry 11 arranged asymmetrically relative tothe longitudinal axis of the said second die aperture 9 and extendingtoward the first die aperture 7. More specifically, a line joining thelongitudinal axes of the first die aperture 7 and a second die aperture9 will bisect the bevelled entry 11 of the said second die aperture 9.Advantageously, the angle between the bevelled entry 11 and the conicalmouth 6 should lie in the approximate range of 4550. Each second dieaperture 9 communicates with a passageway 12 at the rear end of the die5.

Die 5 has been shown with six second die apertures 9 spaced 60 apart. Itwill be understood that die 5 may be provided with fewer or with moresecond die apertures 9 than shown.

The present invention may use die 5 to particular advantage inhydrostatic extrusion apparatus of the type disclosed in US. Pat. No.3,740,985 (1973), although the invention is capable of use with othertypes of ex- 4 trusion apparatus. The said hydrostatic extrusionapparatus will be briefly described hereinbelow to aid in understandingthe present invention.

US. Pat. No. 3,740,985 discloses coating the elongated surface of billetmaterial with a shear transmitting medium which may, for example, bebeeswax or polyethylene wax, and exerting through the shear transmittingmedium a frictional or viscous drag force along the elongated surface ofthe billet material thereby to advance the billet material through a dieto produce extruded product.

The shear transmitting-medium desirably has high viscosity and shearstrength, is capable of lubricating the die, provides good wettingaction on the billet material, and has minimal viscosity variation withrespect to pressure, temperature and shearing rate.

The means which exerts, through the shear transmitting medium, viscousdrag force along the elongated surface of the billet material comprisestrains of gripping element segments, each train being continuouslypropelled by pinion gears around a separate endless path, all of thetrains of grippingelements meeting along one length of travel from afirst station upstream of a die to a second station downstream of thedie and cooperating along said common length of travel to form acontinuously moving train of centrally apertured gripping elementsmoving toward the die. The inner peripheries of the said aperturesengaging the outer surface of the coating of shear transmitting mediumon the billet material generate shear forces in the said medium whichshear forces produce a frictional or viscous drag force along theelongated surface of the billet material to build up axial stress in thebillet material and advance the billet material through the die. Apressure cylinder surrounds the centrally apertured gripping elementsupstream of the die and exerts a normal pressure gradient on'the saidgripping elements increasing toward the die, whereby a normal stressgradient is built up in the billet material increasing toward the die.These axial and normal stresses stress the billet material far above itsyield strength and increase its ductility, or capacity for deformationwithout fracture.

Specific details of the extrusion apparatus are not part of the presentdisclosure. Reference should be made to US. Pat. No. 3,740,985 ifinformation on such details is desired.

In the practice of the present invention with the extrusion apparatusdisclosed in US. Pat. No. 3,740,985, die 5 is supported, as shown inFIG. 4, on die stem 13, the said die stem 13 having apertures extendingtherethrough in registry with apertures 7 and 9 of die 5. The rear ofdie stem 13 is supported on die stem support 14 which is positioned in acounterbore in support plate 15, the latter being mounted to suitableauxiliary supporting structure (not shown). Die stern support 14 andsupport plate 15 are each provided with a central first aperture 17 andwith second apertures 18 surrounding the said first aperture 17, thefirst aperture 17 and the second apertures 18 registering with theapertures in the die stem 13 and hence with first die aperture 7 andsecond die apertures 9, respectively, in die 5.

Valve plate housing 19, having an inwardly directed peripheral flange20, is securely mounted in a suitable manner to the rear of supportplate 15. Valve plate 21, having a central aperture 22 registering withfirst aperture 17in support plate 15 and having second apertures 23adapted to register with second apertures 18 in support plate 15, ispositioned in valve plate housing 19.,

flange retaining said valve plate 21 against the rear of support plate15 with the central aperture 22 aligned with the first aperture 17.Means are provided to rotate valve plate 21 in valve plate housing 19from a position in which all second apertures 23 in the valve plate 21register with all second apertures 18 in support plate 15 to a positionin which all said second apertures 23 have been shifted completely tothe sides of the said second apertures 18 and the said second apertures18 are blocked by the valve plate 21. Advantageously, said means maycomprise, as shown in FIG. 5, a collar 24 mounted on valve plate housing19, a threaded aperture 25 formed in said collar 24 and receiving athreaded shaft 26, a worm gear 27 at the end of the threaded shaft 26,and a geared sector 28 on the periphery of the valve plate 21 meshingwith the worm gear 27. It will be apparent that, by rotating thethreaded shaft 26, valve plate 21 is rotated in valve plate housing 19so as to open or close second apertures 18 in the support plate 15, thefirst aperture 17 in the support plate 15 always being open. Valve platehousing 19, and particularly flange 20, should be strongly constructedso as to resist extrusion forces tending to push valve plate 21 awayfrom support plate 15.

The operation of the invention will now be described.

Threaded'shaft 26 is operated so as to rotate valve plate 21 to aposition in which all second apertures 23 register with all secondapertures 18, i.e., all second apertures 18 are open, in addition tocentral aperture 17 being open. Billet 29, coated with sheartransmitting medium such as beeswax or polyethylene wax, is advanced toand extruded through apertures 7 and 9 of die 5 by means of grippingelement segments 30 propelled toward and past the die 5 by pinion gears(not shown) engaging teeth 31 on the exterior surfaces of the saidgripping element segments 30, in the manner taught in US. Pat. No.3,740,985. The gripping element segments 30 cooperating as a train ofgripping elements constitute a pressure chamber surrounding the billet29 and exert, through the coating of shear transmitting medium, africtional or viscous drag force along the surface of the billet 29thereby advancing the said billet 29 against die 5 and through dieapertures 7 and 9 therein.

It will be understood that, in the manner taught in US. Pat. No.3,740,985, the gripping elements are surrounded upstream of die 5 by apressure cylinder (not shown) whereby a normal stress gradientincreasing toward die 5 and indicated diagrammatically by arrows ofincreasing length in FIG. 4, is applied to the billet 29.

In the foregoing manner, axial and normal stress gradients, increasingtoward die 5 to a value above the yield strength of billet 29, are builtup in the billet 29 as the said billet is advanced, by frictional orviscous drag force along its surface, toward and into die 5 and throughdie apertures 7 and 9 to produce simultaneously a plurality of extrudedwires, wire 32 from aperture 7 and wires 33 from apertures 9. Up to thispoint, the pressure in the shear transmitting medium which may otherwisebe denominated hydrostatic extrusion fluid pressure, and which is aspecific manifestation of what may generically be termed extrusioneffort, rises along curve 34 in FIG. 1 to a level indicateddiagrammatically by the numeral 35.

Thereafter, threaded shaft 26 is operated, while the gripping elementscontinue to drive the billet 29 into and through the die 5, so as toslowly and gradually rotate valve plate 21 to a position in which all ofthe second apertures 18 are blocked off or closed and first aperture 17remains open. Further extrusion of wires 33 will cease, and only wire 32will continue to be ex- 5 truded, and the pressure in the sheartransmitting medium will rise from point 35 along curve 36 to the levelof curve 4 which represents the run-out pressure for single wireextrusion. Wires 33 downstream of valve plate 21 have been shown in FIG.4 in phantom to indicate their temporary or transitory nature in theproduction operation. When the production of wires 33 has ceased, therewill remain in apertures 18 of die stem support and support plate 15, inthe corresponding apertures in the die stem 13 and in second dieapertures 9 of die 5 plugs of the material constituting the billet 29.These plugs, in closing off second die apertures 9, convert the multipleaperture die 5 to a single aperture die for the continued production ofwire 32.

In the operation hereinabove described, pressure peak 2 has beeneliminated, and the extrusion apparatus need be designed only towithstand pressure of the level indicated by curve 4.

.The operation of the apparatus has heretofore been described inconnection with the production of a single wire after all but one of thedie apertures have been closed. It will be understood that the apparatusis not to be considered as being so limited, and that, upon closing theseveral of the die apertures, the remaining die apertures may be keptopen to produce several wires. Thus, if die 5 has seven die apertures asshown, the valve plate may be designed to close down only five of thesedie apertures after commencement of extrusion, leaving two die aperturesopen for the continued production of two wires. As in the previouslydescribed operation, the undesirable transitory pressure peak iseliminated.

What is claimed is:

1. Method of producing wire from a billet, said method comprising:

a. applying force to the billet to commence extrusion of the billetsimultaneously through first die aperture means and second die aperturemeans;

b. after extrusion of the billet simultaneously through the first dieaperture means and the second die aperture means has commenced, andwhile maintaining force on said billet, gradually closing the second dieaperture means;

0. continuing the application of force to said billet to continue theextrusion of said billet through said first die aperture means toproduce wire.

2. Method as in claim 1, wherein:

d. force is applied hydrostatically to said billet.

3. Method of producing wire from a billet, said 55 method comprising:

a. applying force to the billet to commence extrusion of the billetsimultaneously through a plurality of die apertures;

b. after extrusion of the billet simultaneously through the plurality ofdie apertures has commenced, and while maintaining force on said billet,gradually closing all but one of said die apertures;

c. continuing the application of force on said billet thereby tocontinue the extrusion of said billet through the remaining open dieaperture to produce wire.

4. Method as in claim 3, wherein:

(I. force is applied hydrostatically to said billet.

5. Apparatus for extruding a billet to produce wire,

said apparatus comprising:

a. a die having a first die aperture and a second die aperture and aninlet end adapted to receive a billet and communicating with said firstand second die apertures,

b. means for advancing said billet into the inlet end of said die toextrude said billet through said die to produce wire, and

c. means for closing the second die aperture after extrusion hascommenced through both the first and second die apertures such thatextrusion continues only through said first die aperture.

6. Apparatus for extruding a billet to produce wire,

said apparatus comprising:

a. a die having a first die aperture and a plurality of second dieapertures, an inlet end adapted to receive a billet and communicatingwith said first and second die apertures, and an exit end adapted todischarge wire;

b. means for advancing said billet into the inlet end of said die toextrude said billet through said die to produce wire; and

c. valve means for closing the second die apertures after extrusion hascommenced through both the first and second die apertures such thatextrusion continues only through said first die aperture.

7. Apparatus as in claim 6, wherein:

(1. said valve means comprises:

i. a valve plate operatively'associated with the exit end of said die,said valve plate having a plurality of valve plate apertures adapted toregister with all of said second die apertures;

ii. operating means to place said valve plate in a first position inwhich all of said valve plate apertures register with all of said seconddie apertures or selectively in a second position in which all of saidvalve plate apertures are completely out of registry with all of saidsecond die apertures.

8. Apparatus as in claim 6, wherein:

d. said second die apertures surround said first die aperture,

e. said valve means comprises:

i. a valve plate operatively associated with the exit end of said die,said valve plate having a first valve plate aperture registering withsaid first die aperture and a plurality of second valve plate aperturesadapted to register with all of said second die apertures;

ii. operating means to rotate said valve plate to a first position inwhich all of said second valve plate apertures register with all of saidsecond die apertures or selectively to a second position in which all ofsaid second valve plate apertures are completely out of registry withall of said second die apertures.

9. Extrusion die means comprising:

a. a die having a first die aperture and a second die aperture and aninlet end adapted to receive a billet and communicating with said firstand second die apertures, and

b. means for closing the second die aperture after extrusion hascommenced through both the first and second die apertures such thatextrusion continues only through said first die aperture.

10. Extrusion die means comprising:

a. a die having a first die aperture and at least one second dieaperture and an inlet end adapted to receive a billet and communicatingwith said first and second die apertures, and an exit end adapted todischarge wire; and

b. valve means for closing the at least one second die aperture afterextrusion has commenced through both the first and second die aperturessuch that extrusion continues only through said first die aperture.

ll. Extrusion die means as in claim 10, wherein:

c. said valve means comprises:

i. a valve plate operatively associated with the exit end of said die,said valve plate having a plurality of valve plate apertures adapted toregister with all of said second die apertures;

ii. operating means to place said valve plate in a first position inwhich all of said valve plate apertures register with all of said seconddie apertures or selectively in a second position in which all of saidvalve plate apertures are completely out of registry with all of saidsecond die apertures.

12. Extrusion die means as in claim 10, wherein:

c. said second die apertures surround said first die aperture,

d. said valve means comprises:

i. a valve plate operatively associated with the exit end of said die,said valve plate having a first valve plate aperture registeringwithsaid first die aperture and a plurality of second valve plate aperturesadapted to register with all of said second die apertures;

ii. operating means to rotate said valve plate to a first position inwhich all of said second valve plate apertures register with all of saidsecond die apertures or selectively to a second position in which all ofsaid second valve plate apertures are completely out of registry withall of said second die apertures.

UNITED STATES PATENT OFFICE fiERTIFICATE OF CORREQTION PatcntNo.QTQELLJLEQ Dated December 9. 1q75 lnventor(s) FRANCIS JOSEPH FUCHS, JR.Case 111 It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

In the Specification, column 1, line 16, "not Should read --no'w--Column 3, line 30, "by" Should read --be-- Signed and Scaled this 1second Day of March 1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Attesn'ng Officer 4 Commissioner ufPatemsand Trademarks

1. Method of producing wire from a billet, said method comprising: a.applying force to the billet to commence extrusion of the billetsimultaneously through first die aperture means and second die aperturemeans; b. after extrusion of the billet simultaneously through the firstdie aperture means and the second die aperture means has commenced, andwhile maintaining force on said billet, gradually closing the second dieaperture means; c. continuing the application of force to said billet tocontinue the extrusion of said billet through said first die aperturemeans to produce wire.
 2. Method as in claim 1, wherein: d. force isapplied hydrostatically to said billet.
 3. Method of producing wire froma billet, said method comprising: a. applying force to the billet tocommence extrusion of the billet simultaneously through a plurality ofdie apertures; b. after extrusion of the billet simultaneously throughthe plurality of die apertures has commenced, and while maintainingforce on said billet, gradually closing all but one of said dieapertures; c. continuing the application of force on said billet therebyto continue the extrusion of said billet through the remaining open dieaperture to produce wire.
 4. Method as in claim 3, wherein: d. force isapplied hydrostatically to said billet.
 5. Apparatus for extruding abillet to produce wire, said apparatus comprising: a. a die having afirst die aperture and a second die aperture and an inlet end adapted toreceive a billet and communicating with said first and second dieapertures, b. means for advancing said billet into the inlet end of saiddie to extrude said billet through said die to produce wire, and c.means for closing the second die aperture after extrusion has commencedthrough both the first and second die apertures such that extrusioncontinues only through said first die aperture.
 6. Apparatus forextruding a billet to produce wire, said apparatus comprising: a. a diehaving a first die aperture and a plurality of second die apertures, aninlet end adapted to receive a billet and communicating with said firstand second die apertures, and an exit end adapted to discharge wire; b.means for advancing said billet into the inlet end of said die toextrude said billet through said die to produce wire; and c. valve meansfor closing the second die apertures after extrusion has commencedthrough both the first and second die apertures such that extrusioncontinues only through said first die aperture.
 7. Apparatus as in claim6, wherein: d. said valve means comprises: i. a valve plate operativelyassociated with the exit end of said die, said valve plate having aplurality of valve plate apertures adapted to register with all of saidsecond die apertures; ii. operating means to place said valve plate in afirst position in which all of said valve plate apertures register withall of said second die apertures or selectively in a second position inwhich all of said valve plate apertures are completely out of registrywith all of said second die apertures.
 8. Apparatus as in claim 6,wherein: d. said second die apertures surround said first die aperture,e. said valve means comprises: i. a valve plate operatively associatedwith the exit end of said die, said valve plate having a first valveplate aperture registering with said first die aperture and a pluralityof second valve plate apertures adapted to register with all of saidsecond die apertures; ii. operating means to rotate said valve plate toa first position in which all of said second valve plate aperturesregister with all of said second die apertures or selectively to asecond position in which all of said second valve plate apertures arecompletely out of registry with all of said second die apertures. 9.Extrusion die means comprising: a. a die having a first die aperture anda second die aperture and an inleT end adapted to receive a billet andcommunicating with said first and second die apertures, and b. means forclosing the second die aperture after extrusion has commenced throughboth the first and second die apertures such that extrusion continuesonly through said first die aperture.
 10. Extrusion die meanscomprising: a. a die having a first die aperture and at least one seconddie aperture and an inlet end adapted to receive a billet andcommunicating with said first and second die apertures, and an exit endadapted to discharge wire; and b. valve means for closing the at leastone second die aperture after extrusion has commenced through both thefirst and second die apertures such that extrusion continues onlythrough said first die aperture.
 11. Extrusion die means as in claim 10,wherein: c. said valve means comprises: i. a valve plate operativelyassociated with the exit end of said die, said valve plate having aplurality of valve plate apertures adapted to register with all of saidsecond die apertures; ii. operating means to place said valve plate in afirst position in which all of said valve plate apertures register withall of said second die apertures or selectively in a second position inwhich all of said valve plate apertures are completely out of registrywith all of said second die apertures.
 12. Extrusion die means as inclaim 10, wherein: c. said second die apertures surround said first dieaperture, d. said valve means comprises: i. a valve plate operativelyassociated with the exit end of said die, said valve plate having afirst valve plate aperture registering with said first die aperture anda plurality of second valve plate apertures adapted to register with allof said second die apertures; ii. operating means to rotate said valveplate to a first position in which all of said second valve plateapertures register with all of said second die apertures or selectivelyto a second position in which all of said second valve plate aperturesare completely out of registry with all of said second die apertures.